Cover for protecting solar cells during fabrication

ABSTRACT

A removable cover system for protecting solar cells from exposure to moisture during fabrication processes. The cover system includes a cover having a configuration that complements the configuration of a solar cell substrate to be processed in an apparatus where moisture is present. A resiliently deformable seal member attached to the cover is positionable with the cover to engage and seal the top surface of the substrate. In one embodiment, the cover is dimensioned and arranged so that the seal member engages the peripheral angled edges and corners of the substrate for preventing the ingress of moisture beneath the cover. An apparatus for fabricating a solar cell using the cover and associated method are also disclosed.

FIELD

The present disclosure generally relates to thin film solar cells, andmore particularly to a cover for temporarily the solar cell andsemiconductor layers formed thereon on during fabrication processes.

BACKGROUND

Thin film photovoltaic (PV) solar cells are one class of energy sourcedevices which harness a renewable source of energy in the form of lightthat is converted into useful electrical energy which may be used fornumerous applications. Thin film solar cells are multi-layeredsemiconductor structures formed by depositing various thin layers andfilms of semiconductor and other materials on a substrate. These solarcells may be made into light-weight flexible sheets in some formscomprised of a plurality of individual electrically interconnectedcells. The attributes of light weight and flexibility gives thin filmsolar cells broad potential applicability as an electric power sourcefor use in portable electronics, aerospace, and residential andcommercial buildings where they can be incorporated into variousarchitectural features such as roof shingles, facades, and skylights.

Thin film solar cell semiconductor packages generally include aconductive back contact or electrode formed on a rear glass or polymersubstrate and a conductive front contact or electrode formed above theback electrode. Front electrodes have been made for example of lighttransmittance conductive oxide (“TCO”) film materials. A light-absorbingactive or absorber layer (“ABS”) is interspersed between front and backelectrodes which absorbs the solar radiation photons and exciteselectrons to produce an electric current thereby chemically convertingsolar energy into electrical energy.

Processes used to form absorber layers made of chalcogenide materialssuch as copper indium diselenide species (CIS), copper indium galliumdiselenide species or Cu(In,Ga)Se₂ (“CIGS”) or Cu(In,Ga)(Se, S)₂(“CIGSS”) involve a furnace-based selenization/sulfurization process.Generally, base materials such as copper, indium, and gallium (for CIGSor CIGGS absorber layers) are sputtered or otherwise deposited on theback electrode of the solar cell substrate. The substrate is then loadedinto a furnace where a carrier gas containing selenide is introducedfollowed by introducing gas containing sulfide, all of which is coupledwith heating.

In additional processes used in forming the thin film solar cell, bufferlayers made of cadmium sulfide (CdS) are formed on the absorber layercommonly by a chemical bath deposition (CBD) process wherein the entiresubstrate is immersed in an electrolytic chemical bath.

The foregoing selenization/sulfurization and CBD processes createunwanted carryover and formation of chemical compound deposits on solarcell surfaces other than the intended target areas. Accordingly, it isgenerally desirable after forming the foregoing absorber and bufferlayers to etch and clean the backside surface of the rear glasssubstrate to remove any chemical compound debris or deposits that mayhave adhered to and contaminated this surface to avoid potentialperformance degradation of the solar cell or appearance defects. Therear substrate backside etching/cleaning operations use a combination ofchemical etching, brushing, and water. Chalcogenide absorber layer filmsformed on the opposite side of the rear glass substrate, however, aresusceptible to peeling and other forms of damage if exposed to moisture,water, and etching solutions. This can cause appearance defects and moresignificantly adversely affects the reliability of the solar cell.Therefore, it is useful to protect the absorber layer from exposure towater and moisture when cleaning the rear substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the exemplary embodiments will be described withreference to the following drawings where like elements are labeledsimilarly, and in which:

FIG. 1 is a cross-sectional side view of a first embodiment of a thinfilm solar cell according to the present invention;

FIG. 2 is a flow chart showing sequential steps in an exemplary processfor the formation thereof;

FIG. 3 is a schematic side elevation drawing of a conventional substratebackside wet etching/cleaning apparatus;

FIG. 4 is a cross-sectional side elevation view of a conventionalprotective substrate cover used in the apparatus of FIG. 3;

FIG. 5 is a top plan view showing the configuration of a substrate andcover of FIG. 4;

FIG. 6 is a side elevation view of the corner region of the substrateand cover combination of FIG. 5 taken along line 6-6 in FIG. 5;

FIG. 7 is a top plan view showing the configuration of a substrate and aprotective cover according to the present disclosure;

FIG. 8 is a cross-sectional side elevation view of the cover of FIG. 7on a substrate;

FIG. 9 is an enlarged detailed side elevation view taken from FIG. 8,with a seal member being shown in an uncompressed state positioned on ornear the substrate;

FIG. 10 is an enlarged detailed side elevation view thereof, with theseal member being shown in a compressed state against the substrate;

FIGS. 11-15 are cross-sectional perspective views of several embodimentsof seal members useable with the cover of FIG. 9; and

FIG. 16 is an enlarged detailed side elevation view of the protectivecover of FIG. 9 showing an alternative mounting arrangement of the sealmember.

All drawings are schematic and are not drawn to scale.

DETAILED DESCRIPTION

This description of illustrative embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. In the description ofembodiments disclosed herein, any reference to direction or orientationis merely intended for convenience of description and is not intended inany way to limit the scope of the present disclosure. Relative termssuch as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,”“up,” “down,” “top” and “bottom” as well as derivative thereof (e.g.,“horizontally,” “downwardly,” “upwardly,” etc.) should be construed torefer to the orientation as then described or as shown in the drawingunder discussion. These relative terms are for convenience ofdescription only and do not require that the apparatus be constructed oroperated in a particular orientation.

Terms such as “attached,” “affixed,” “coupled,” “connected” and“interconnected,” refer to a relationship wherein structures are securedor attached to one another either directly or indirectly throughintervening structures, as well as both movable or rigid attachments orrelationships, unless expressly described otherwise. Moreover, thefeatures and benefits of the disclosure are illustrated by reference tothe embodiments. Accordingly, the disclosure expressly should not belimited to such embodiments illustrating some possible non-limitingcombination of features that may exist alone or in other combinations offeatures.

FIG. 1 is a cross-sectional view of an exemplary embodiment of a thinfilm solar cell 100. Solar cell 100 basically includes a rear substrate110, a bottom electrode layer 120 formed thereon, an absorber layer 130formed thereon, a buffer layer 140 formed thereon, and a TCO topelectrode layer 150 formed thereon. Additional layers and structures maybe built above layer 150 to complete the solar cell. As further shownfor example in FIGS. 6, 7, and 9, the substrate 110 has a perimeterdefined by upper peripheral angled edges 111 extending horizontallyaround the entire substrate at the top of vertical sides 112 of thesubstrate (shown in FIGS. 6 and 7). Referring to FIGS. 6, 7, and 9, theedges 111 are angled at 90 degrees in some embodiments forming a pointin cross-section (see, e.g. FIG. 9) and corresponding linear edge thatextends horizontally completely around the entire perimeter of thesubstrate (see, e.g. FIG. 7).

Solar cell 100 further includes micro-channels which are patterned andscribed into the semiconductor structure to interconnect the variousconductive material layers and to separate adjacent solar cells. Thesemicro-channels or “scribe lines” as commonly referred to in the art aregiven “P” designations related to their function and step during thesemiconductor solar cell fabrication process. P1 scribe linesinterconnect the absorber layer 130 to the substrate 110. P2 scribe lineforms a conductive connection between the bottom and top electrodes 120and 150. P3 scribe lines extend completely through the foregoing solarcell layers to the rear substrate 110 to isolate adjacent solar cells.

An exemplary method for forming solar cell 100 is shown in thesequential steps in FIG. 2.

Referring now to FIGS. 1 and 2, rear substrate 110 is first cleaned instep 200 by any suitable means used in the art to prepare the substratefor receiving the bottom electrode layer. In one embodiment, substrate110 may be cleaned by using detergent or chemical in either brushingtool or ultrasonic cleaning tool.

Suitable materials that may be used for rear substrate 110 includewithout limitation glass such as for example without limitation sodalime glass, ceramic, metals such as for example without limitation thinsheets of stainless steel and aluminum, or polymers such as for examplewithout limitation polyamides, polyethylene terephthalates, polyethylenenaphthalates, polymeric hydrocarbons, cellulosic polymers,polycarbonates, polyethers, and others. In one embodiment, glass may beused for rear substrate 110.

Next, bottom electrode layer 120 is then formed on a substrate 110 (step205) by any method used in the art including without limitationsputtering, atomic layer deposition (ALD), chemical vapor deposition(CVD), or other techniques.

In one embodiment, bottom electrode layer 120 may be made of molybdenum(Mo); however, other suitable electrically conductive metallic andsemiconductor materials used in the art may be used such as Al, Ag, Sn,Ti, Ni, stainless steel, ZnTe, etc.

In some representative embodiments, without limitation, bottom electrodelayer 120 may preferably have a thickness ranging from about andincluding 0.1 to 1.5 microns (μm). In one embodiment, layer 120 has arepresentative thickness on the order of about 0.5 μm.

With continuing reference to FIGS. 1 and 2, P1 patterned scribe linesare next formed in bottom electrode layer 120 (step 210) to expose thetop surface 113 of substrate 110 as shown. Any suitable scribing methodcommonly used in the art may be used such as without limitationmechanical scribing with a stylus or laser scribing.

A p-type doped semiconductor light absorber layer 130 is next formed ontop of bottom electrode layer 120 (step 215). The absorber layer 130material further fills the P1 scribe line and contacts the exposed topsurface 113 of substrate 110 to interconnect layer 130 to the substrate,as shown in FIG. 1.

In some embodiments, absorber layer 130 is a p-type doped chalcogenidematerial commonly used in the art, such as without limitationCu(In,Ga)Se₂ or “CIGS.” Other suitable chalcogenide materials may beused including without limitation Cu(In,Ga)(Se, S)₂ or “CIGSS,” CuInSe₂,CuGaSe₂, CuInS₂, Cu(In,Ga)S₂, or other combinations of elements of groupII, III or VI of the periodic table of elements. In some representativeembodiments, without limitation, absorber layer 130 may preferably havea thickness ranging from about and including 0.5 to 5.0 microns (μm). Inone embodiment, absorber layer 130 has a representative thickness on theorder of about 2 μm.

Absorber layer 130 formed of CIGS may be formed by any suitable vacuumor non-vacuum process used in the art. Such processes include, withoutlimitation, selenization, sulfurization after selenization (“SAS”),evaporation, sputtering electrodeposition, chemical vapor deposition,ink spraying, etc. (step 215).

The selenization and sulfurization processes of step 215 when usedtypically leave deposits or residues of organic and/or inorganiccompounds on the backside or bottom surface 114 of rear substrate 110(identified in FIG. 4) which is removed by a substrate backside cleaningprocess (step 219). Such cleaning processes generally include acombination of chemical etching with mechanical brushing and watercleansing of the backside substrate surface. This cleaning process isfurther described in detail below.

With continuing reference now to FIGS. 1 and 2, an n-type buffer layer140 which may be CdS (cadmium sulfide) is then formed on absorber layer130 to create an electrically active n-p junction (step 220). Bufferlayer 140 may be formed any suitable method commonly used in the art. Inone embodiment, buffer layer 140 may be formed by an electrolytechemical bath deposition (CBD) process using an electrolyte solutionthat contains sulfur. In some representative embodiments, withoutlimitation, buffer layer 140 may preferably have a thickness rangingfrom about and including 0.005 to 0.15 microns (μm). In one embodiment,buffer layer 140 has a representative thickness on the order of about0.015 μm.

The CBD process of forming CdS buffer layer also typically leavesdeposits or residues of organic and/or inorganic chemical compounds onthe backside or bottom surface 114 of rear substrate 110, which isremoved by repeating the same substrate cleaning process (step 222)previously noted above following sulfurization and selenizationprocesses (step 215) used in some embodiments for forming absorber layer130. This cleaning process is further described in detail below.

After forming CdS buffer layer 140, the P2 scribe lines are next cutthrough the absorber layer 130 to expose the top surface 113 of thebottom electrode 120 within the open scribe line or channel (step 225).Any suitable method used in the art may be used to cut the P2 scribeline as previously described, including without limitation mechanical(e.g. cutting stylus) or laser scribing. The P2 scribe line will laterbe filled with a conductive material of top electrode layer 150 tointerconnect the top electrode to the bottom electrode layer 120.

With continuing reference to FIGS. 1 and 2, after forming the P2 scribelines, a light transmitting n-type doped top electrode layer 150preferably made of a TCO material is next formed on top of buffer layer140 for collecting current (electrons) from the cell and preferablyabsorbing a minimal amount of light which passes through to the lightabsorbing layer 130 (step 230). This creates additional active surfacearea for the collection of current by the top electrode which carriesthe charge to an external circuit. The P2 scribe line is also at leastpartially filled with the TCO material as shown in FIG. 1 on thevertical sidewalls of the P2 line and on top of bottom electrode layer120 therein to form an electrical connection between the top electrodelayer 150 and bottom electrode 120 creating an electron flow path.

Aluminum (Al) and Boron (B) are two possible n-type dopant that iscommonly used for TCO top electrodes in thin film solar cells; however,others suitable dopants may be used such as without limitation Aluminum(Al), Boron (B), Gallium (Ga), Indium (In) or other elements of groupIII of the periodic table.

In one embodiment, the TCO used for top electrode layer 150 may be anymaterial commonly used in the art for thin film solar cells. SuitableTCOs that may be used include without limitation zinc oxide (ZnO), Borondoped ZnO (“BZO”), Aluminum doped ZnO (“AZO”), Gallium doped ZnO(“GZO”), Indium doped ZnO (“IZO”), fluorine tin oxide (“FTO” or SnO₂:F),or indium tin oxide (“ITO”). Top electrode layer 150 may be formed ofany other suitable coating materials possessing the desired propertiesfor a top electrode, such as a carbon nanotube layer. In one embodiment,the TCO used is BZO.

In some embodiments where top electrode layer 150 may be made of Borondoped ZnO or “BZO”, it should be noted that a thin intrinsic ZnO filmmay form on top of absorber layer 130 (not shown) during formation ofthe thicker n-type doped TCO top electrode layer 150.

With continuing reference to FIGS. 1 and 2, following formation of TCOtop electrode layer 150, the P3 scribe line is formed in thin film solarcell 100 (step 240). The P3 scribe line extends through (from top tobottom) top electrode layer 150, buffer layer 140, absorber layer 130,and the bottom electrode layer 120 down to the top of substrate 110 asshown.

Additional final back end steps are then taken to complete the solarcell module, which are well known and understood by those skilled in theart. This includes laminating a top cover (not shown), such as a glasscover, onto the cell structure with a suitable encapsulant such aswithout limitation a combination of EVA (ethylene vinyl acetate) andbutyl to seal the solar cell (steps 245 and 250 in FIG. 2).

Further back end processes (step 255) are performed which may includeforming front conductive grid contacts and one or more anti-reflectivecoatings (not shown) above top electrode 150 by a manner known in theart. The grid contacts will protrude upwards through and beyond the topsurface of any anti-reflective coatings for connection to externalcircuits. This produces a completed solar cell module (step 260).

Backside Etching and Cleaning Apparatus

FIG. 3 is a schematic diagram of apparatus 300 that is useable forperforming the rear substrate 110 backside etching and cleaningoperations shown in steps 219 and 222 in FIG. 2 and described above. Theapparatus 300 embodies an inline process system that includes a loadingsection 302, wet etch process section 310, wet rinsing or shower section320, an air blow or dry section 330, and unloading section 304.Apparatus 300 includes an elongated process enclosure 306 extendinglongitudinally from the loading section 302 to unloading section 304 asshown. This creates a controlled environment around the solar cell 100(or partially formed solar cell) for performing the sequential etching,rinsing, and air drying operations. The apparatus 300 includes allappropriate and necessary auxiliary equipment to perform each operationsuch as, for example, liquid chemical storage and dispensing equipment,pumps, motors, brushes, blower/fans, wiping blades, power supply,controls, etc. Etching and cleaning apparatuses as diagrammaticallyshown are commercially available such as VITRUM-Etch 2000 andVITRUM-Clean 2000 tools from Singulus of Kahl, Germany.

During the etching and cleaning process, solar cell substrates 110 arereceived in the loading section 302 shown in FIG. 3 at the left. At step219 in the solar cell 100 fabrication process shown in FIG. 2, theabsorber layer 130 has already been formed on rear substrate 110 (step215) and underwent processing in the selenization furnace therebyrequiring removal of unwanted residual chemical compound deposits fromthe backside (i.e. bottom surface 114, FIG. 6) of the substrate (step219). This would be a first etching/cleaning operation on the solar cell100. Alternatively, the CdS buffer layer 140 may have just been formedvia CBD (step 220) before a second etching/cleaning operation (step222). In either case of a first or second cleaning operation (step 219or 222), the substrate 110 with absorber layer 130 formed on theopposing front side of substrate 110 requires protection from theetching/cleaning process as described above on the backside.

Referring to FIGS. 3 and 4, a protective cover 340 is placed on top ofsubstrate 110 in the loading chamber 302. FIG. 4 is an enlarged viewfrom FIG. 3 showing the cover in the process of being positioned on thesubstrate (see downward arrow). The cover 340 may be supported andconnected temporarily to apparatus for loading into the wet etch processsection 310, and unloading from the air blow or dry section 330 by asuitable structural frame 311 of appropriate configuration. Theapparatus 300 includes a cover handling system which is configured andoperable to raise and lower cover 340 via the frame 311, and to maintainengagement between the cover 340 and substrate 110 during processing.The cover 340 is pressed downwards onto an upper flat perimeter portionof the top surface 113 of the substrate 110 (see FIGS. 4 and 6) in thecover loading section 302. A peripheral seal 342 of the slice-typeo-ring style extends completely around the perimeter of the cover 340 iscompressed against the upper surface to form a seal to protect absorberlayer 130 within the cover 340 during the etching and cleaning processesto follow. This type seal has an outwardly flared section (typicallydisposed at about 45 degrees) as shown in FIG. 4 which folds upward andflattens when pressed downward against the substrate.

Next in the etching/cleaning process (steps 219 or 222 in FIG. 2), theprotected substrate 110 with cover 340 in place flows from left to rightin FIG. 3 and first moves through the wet etch process section 310 ofthe apparatus 300 to removed the chemical compounds from the backside orbottom surface 114 of rear substrate 110. In some embodiments, thesubstrates 110 may move automatically on a conveyor (schematicallyrepresented by the plurality of rollers 308) through apparatus 300. Thecover handling system releases cover 340 after it leaves the loadingsection 302 and enters process section 310. The apparatus 300 maintainspressure against the cover, which remains sealed with substrate 110. Acombination of wet or liquid etching chemicals such as H₂O₂ (hydrogenperoxide) and/or others dispensed by a plurality of chemical spraynozzles 314 and mechanical brushing of the backside of substrate 110 bya plurality of brushes 312 are used to removed the chemical compounddeposits from the backside surface of the substrate 110.

With continuing reference to FIG. 3, the protected substrate 110 nextmoves through the wet rinsing or shower section 320 where a plurality ofdeionized water (DI) spray nozzles 322 wet the exposed portions of thesubstrate and cover 340 to rinse away any residual etching chemicals.After rinsing, the substrate 110 moves through the air blow or drysection 330 where one or more blowers 332 drive high pressure clean airacross the cover 340 and exposed portions of the substrate to removesignificant amounts of residual water and moisture. The substrate 110next moves into the unloading section 304 as shown at right. At thispoint, the substrate 110 has left the active process sections orchambers 310, 320, and 330 and the protective cover 340 may now belifted off of the substrate by the cover handling system via frame 311.The apparatus 300 returns the cover 340 to the loading section 302 forapplication to another substrate to be processed for backsideetching/cleaning.

In certain circumstances, the protective cover 340 shown in FIGS. 3 and4 may not be completely effective at preventing infiltration of someamount of liquid chemicals and/or water underneath the cover duringbackside etching/cleaning. The liquid chemicals and/or water cansometimes find a leakage pathway beneath the seal and reach the absorberlayer 130 and damage aesthetically and structurally the absorber layer130 as well as compromising performance of the solar cell beingfabricated. Several factors may contribute to such leakage.

For example, solar cell substrates 110 are typically rectangular inconfiguration as shown in FIG. 5. Conversely, the protective covers 340may not conform perfectly in configuration particularly along the entireperimeter to the shape of the substrate 110, and in some embodiments thecover may have rounded or arcuate corners as shown in FIG. 5. When thecover is placed on the substrate as described above, the corner portionson the top surface 113 of substrate 110 remain exposed as shown to theapparatus 300 wet processes described herein. This creates exposed flatupper corner 115 surface areas where the liquid chemicals and/or waterdispensed at pressure both above and below the substrate may pond orpool and be driven underneath the seal 342 to reach the absorber layer130 (see, e.g. FIG. 6). Rinse water remaining on these exposed corner115 surface areas of substrate 110 may similarly be driven underneathseal 342 in the air dry section 330 by the high pressure blowersanalogously to wind-driven rain. Since the seal 342 engages the top flatsurface 113 of the substrate 110 at least at the corners due thenon-conformal shaped cover 340 (i.e. flat-to-flat surface contact),slight surface imperfections on the top surface 113 beneath the seals342 can create pathways for moisture and liquid to leak underneath thecover and reach absorber layer 130.

To minimize or eliminate the foregoing potential leakage problems, FIGS.7-10 show various embodiments of a protective cover system including aconformal cover 400 and seal member 420 according to the presentdisclosure. Unlike the foregoing cover 340 system shown for example inFIGS. 5 and 6, cover 400 is configured to form a water-resistant sealbetween the linear-shaped upper angled edge 111 of substrate 110 andseal member 420 directly (see FIG. 8) instead of the flat top substratesurface 113 to seal 342 interface as in cover 320 (see FIG. 6). Thisedge sealing interface according to the present disclosure providesimproved protection against moisture penetration and eliminates any flatexposed top surface 113 areas on the substrate 110 (particularly atcorners 115) which pool liquid that can enter beneath the cover seal asdescribed above. The peripheral angled edges 111 of substrate 110provided linear engagement with seal member 420 that creates awater-tight seal with the cover 400.

Referring to the top view in FIG. 7, to achieve the edge sealingparticularly at the corners 115 of rear substrate 110, the peripheraledges of cover 400 conforms to and complements the shape (in top orplanar view as shown) of the substrate 110. In various embodiments, forexample without limitation, cover 400 may have rectangular, rectangularwith rounded corners, polygonal, or circular shapes depending on theshape of the substrate. In the embodiments shown, the shapes of cover400 and substrate 110 are rectangular. The four corners 401 of cover 400particularly matches the configuration of the corners 115 of substrate110 (in top plan view) to achieve edge sealing all the way around theperimeter of the substrate (see FIG. 7).

Dimensionally, cover 400 has an outer size of length and width that isthe same or slightly larger than the length and width of substrate 110.In various embodiments, the seal member 420 is attached to the cover 400and still engage the linear edge of substrate 110, the cover is slightlylarger in width and length than the substrate to accommodate the sealingmember 420.

Protective cover 400 may be made of any suitable material includeplastics or metals. In one embodiment, cover 400 is made ofpolycarbonate, which may be clear or opaque. Accordingly, cover 400 maybe of unitary construction and formed by any suitable process includingmolding, casting, stamping, pressure extrusion, etc depending on thematerial used. The cover 400 has a suitable thickness to provide thestructural strength needed to form a substantially rigid cover instructure to resist bending, deflection, or warping during processing inapparatus 300 which might otherwise compromise the leak-resistantperformance of the cover system.

Referring to FIGS. 8-10, covers 400 include a generally horizontal topsection 402 and vertical sidewalls 404 extending downwardly from the topsection 402. The vertical sidewalls 404 define an internal cavity 408 ofsufficient height and area to cover substrate 110 therein withoutdamaging any solar cell layers already formed thereon such as absorberlayer 130. In some embodiments, the sidewalls 404 define a peripheraledge and perimeter of the cover 400. In one embodiment, top section 402is substantially flat or slightly domed. Sidewalls 404 may be orientedperpendicular to top section 402 or be slightly angled, as shown. Aperipheral bottom surface 406 is formed at the bottom edge of andunderneath each sidewall 404 that extends around the perimeter of cover400. Bottom surface 406 has a sufficient width to allow the cover 400 torest with stability on substrate 110 and to accommodate the lateralwidth of seal member 420 that is to the bottom surface 406.

According to various embodiments, seal member 420 is a highlycompressible and deformable elastomeric member with a great degree ofresiliency in configuration and structure to maximize the effectivenessof the temporary sealing of protective cover 400 to the peripheral edgesof substrate 110 during backside substrate etching/cleaning in apparatus300 of FIG. 3. In some embodiments, seal member 420 is made of a foamrubber, for example, EDPM (Ethylene-Propylene-Diene Monomer) closed cellsponge. EPDM possesses the desired compressible and resiliency or memorycharacteristics for a leak-resistant seal over repeated cycles ofcompression and expansion. Other highly deformable seal materials may beused such as without limitation natural or synthetic rubber, siliconerubber, butyl rubber, neoprene rubber, or NBR (Nitrile butadiene rubber)of suitable configuration.

In operation, apparatus 300 initially positions cover 400 onto substrate110 wherein seal member 420 is located proximate to, or slightlyengages, edge 111 of the substrate as shown in FIGS. 8 and 9. Sealmember 420 is in an undeformed and uncompressed state as best shown inFIG. 9. The cover 400 is then pressed downwards against substrate 110wherein edge 111 of the substrate deforms and at least partiallycompresses seal member 420 (see FIG. 10) sufficiently to produce aleak-resistant seal around the peripheral edges of the substrate. Sealmember 420 is in a compressed state and operative to seal the cover 400to the substrate 110 to begin the backside cleaning process.

Seal member 420 may have numerous cross-sectional configurationsincluding open structures of varying configurations such as shown inFIGS. 11-13 having an open central region surrounded by a wall of sealmaterial, or closed solid structures of varying configurations such asshown in FIGS. 14-15. The structural type (i.e. open or closed) andcross-sectional configuration will depend in part on the method selectedto attach the seal member 420 to cover 400, degree of deformabilitydesired, and configuration and size of the sidewall bottom surface 406provided. In some embodiments, seal member 420 has the generalconfiguration of an O-ring or modified O-ring shape as shown in FIGS.11-13. In one embodiment, seal member 420 is an O-ring with a has aD-shape cross-section as shown in FIG. 13.

Seal member 420 has a length suitable to extend completely around theperimeter of cover 400 on sidewall bottom surface 406 so that there areno gaps present through which moisture may infiltrate beneath the coverto reach absorber layer 130 on substrate 110. Accordingly, the totalcombined length of seal member 420 is the same as the total combinedlength of the peripheral angled edge 111 of substrate 110 extendingcompletely around the substrate. The seal member 420 may be spliced,mitered, or otherwise joined together such as at the corners 401 ofcover 400 to form a continuous loop seal extending around the entireperimeter of the cover.

Seal member 420 may be attached to bottom surface 406 of cover 400 byany suitable means including adhesives in some embodiments.Configurations of seal member 420 having a flat side or surface such asshown in FIGS. 12, 13, and 15 may be easily attached using an adhesivewhen the bottom surface 406 has a flat profile. In other embodiments asshown in FIG. 16, the bottom surface 406 includes a mounting groove 401to receive a portion of seal member 420 secure the seal in position oncover 400 via a frictional fit in addition to or instead of usingadhesives. Any of the cross-sectional configurations of seal membersshown may be used with a mounting groove 401. Particularly, the sealswithout a flat side or surface such as those shown in FIGS. 11 and 14may be used in a more secure seal with a mounting groove by positivelylocating the seal in the sidewall bottom surface 406.

In some embodiments, the cover 400 and seal member 420 are configuredand arranged so that the upper peripheral angled edges 111 of substrate110 will engages the seal proximate to the midpoint of the seal as shownin FIGS. 9, 10, and 16 for maximum deformation and sealingeffectiveness.

It will be appreciated that the embodiments of the protective coversystem described herein are not only suitable for providing protectivemoisture barriers for CIGS-based absorber layer solar cells, but mayalso be used with equal benefit for CdTe-based and other type thin filmsolar cells which may be susceptible to moisture damage.

According to one aspect of the present disclosure, a removable coversystem for protecting solar cell substrates during fabrication processesis provided. The solar cell substrate has a top surface, bottom surface,and a perimeter defined by peripheral angled edges extendinghorizontally around the solar cell substrate. The cover system includesa cover having a top section and peripheral sidewalls that form aninternal cavity, the peripheral sidewalls defining a perimeter whichextends horizontally around the cover, the perimeter being approximateto the perimeter of the solar cell substrate, and a resilientlydeformable seal member attached to the sidewalls and extending aroundthe perimeter of the cover, wherein the seal member is configured toseal the top surface of the solar cell substrate at the peripheralangled edges when the cover is engaged to the solar cell substrate. Inone embodiment, when the cover is placed on the substrate, the cover isdimensioned and arranged so that the seal member engages the peripheralangled edges of the substrate for preventing the ingress of moisturebeneath the cover. In one embodiment, the solar cell substrate has arectangular or square configuration with square corners formed betweentwo opposing pairs of peripheral angled edges, and the cover has amatching rectangular or square configuration with square corners formedbetween two opposing pairs of sidewalls. In one embodiment, theperimeter of the cover is configured and dimensioned to have acomplementary shape to the solar cell substrate so that the covercompletely covers the top surface of the substrate when placed thereon.

According to another aspect of the present disclosure, a solar cellfabrication process apparatus is provided. A solar cell fabricationprocess apparatus includes a process enclosure including at least onewet solar cell fabrication process, a cover having a top section andperipheral sidewalls that form an internal cavity, the peripheralsidewalls defining a perimeter which extends horizontally around thecover, the perimeter being approximate to a perimeter of a partiallyfabricated solar cell substrate. The apparatus further includes aresiliently deformable seal member attached to the sidewalls andextending around the perimeter of the cover, and a frame attachable tothe cover and connected to the apparatus. The apparatus is operable tolower the cover into a closed position engaged with a top surface of thesolar cell substrate and to raise the cover off of the top surface ofthe solar cell substrate into an open position disengaged with the solarcell substrate. The seal member is configured to seal the top surface ofthe solar cell substrate at the peripheral angled edges when the coveris at the closed position.

According to yet another aspect of the present disclosure, a method forfabricating solar cells is provided. The method includes: depositing aconductive bottom electrode layer on a top surface of a substrate;depositing an absorber layer on the bottom electrode layer; performingselenization on the absorber layer; protecting the absorber layer byplacing a protective cover on the top surface of the substrate, whereina resiliently deformable seal member on the cover engages peripheralangled edges of the substrate to effectuate a leak-resistant seal; andwet etching a bottom surface of the substrate with the protective coverpositioned on the top surface of the substrate to remove selenizationcompound deposits

While the foregoing description and drawings represent exemplaryembodiments of the present disclosure, it will be understood thatvarious additions, modifications and substitutions may be made thereinwithout departing from the spirit and scope and range of equivalents ofthe accompanying claims. In particular, it will be clear to thoseskilled in the art that various embodiments according to the presentdisclosure may be configured in other forms, structures, arrangements,proportions, sizes, and with other elements, materials, and components,without departing from the spirit or essential characteristics thereof.In addition, numerous variations in the exemplary methods and processesdescribed herein may be made without departing from the presentdisclosure. The presently disclosed embodiments are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the claimed invention being defined by the appended claims andequivalents thereof, and not limited to the foregoing description orembodiments.

What is claimed is:
 1. A removable cover system for protecting a solarcell substrate during a fabrication process, the solar cell substratehaving a top surface, bottom surface, and a perimeter defined byperipheral angled edges extending horizontally around the solar cellsubstrate, the system comprising: a cover having a top section andperipheral sidewalls that form an internal cavity, the peripheralsidewalls defining a perimeter which extends horizontally around thecover, the perimeter being approximate to the perimeter of the solarcell substrate; a resiliently deformable seal member attached to thesidewalls and extending around the perimeter of the cover, wherein theseal member is configured to seal the top surface of the solar cellsubstrate at the peripheral angled edges when the cover is engaged tothe solar cell substrate.
 2. The cover system of claim 1, wherein thesolar cell substrate has a rectangular or square shape.
 3. The coversystem of claim 2, wherein the cover has a length and width that isdimensioned to be at least the same as or larger than a correspondinglength and width of the solar cell substrate.
 4. The cover system ofclaim 1, wherein the seal member is attached to a bottom surface of theperipheral sidewalls of the cover.
 5. The cover system of claim 1,wherein the seal member is made of closed cell Ethylene-Propylene-DieneMonomer.
 6. The cover system of claim 1, wherein the seal memberincludes foam rubber.
 7. The cover system of claim 1, wherein the sealmember is configured to engage the peripheral angled edges of the solarcell substrate about mid-way between lateral sides of the seal member.8. The cover system of claim 1, wherein the seal member has across-sectional shape having an empty center.
 9. The cover system ofclaim 8, wherein the seal member has a cross-sectional shape selectedfrom the group consisting of an o-ring and a d-ring.
 10. The coversystem of claim 1, wherein the top surface of the solar cell substrateincludes an absorber layer, the absorber layer being positioned beneaththe cover and interior to the seal member when the cover is engaged tothe solar cell substrate.
 11. The cover system of claim 1, wherein theperimeter of the cover is configured and dimensioned so that the covercompletely covers the top surface of the substrate when placed thereon.12. A solar cell fabrication process apparatus comprising: a processenclosure including at least one wet solar cell fabrication process; acover having a top section and peripheral sidewalls that form aninternal cavity, the peripheral sidewalls defining a perimeter whichextends horizontally around the cover, the perimeter being approximateto a perimeter of a partially fabricated solar cell substrate; aresiliently deformable seal member attached to the sidewalls andextending around the perimeter of the cover; a frame attachable to thecover and connected to the apparatus, the apparatus being operable tolower the cover into a closed position engaged with a top surface of thesolar cell substrate and to raise the cover off of the top surface ofthe solar cell substrate into an open position disengaged with the solarcell substrate; wherein the seal member is configured to seal the topsurface of the solar cell substrate at the peripheral angled edges whenthe cover is at the closed position.
 13. The apparatus of claim 12,wherein the apparatus is operable to apply a downward force to the coverat the closed position.
 14. The apparatus of claim 12, wherein the atleast one wet solar cell fabrication process is wet substrate backsideetching performed on a bottom surface of the substrate.
 15. Theapparatus of claim 12, wherein the solar cell substrate has arectangular or square shape.
 16. The apparatus of claim 12, wherein thecover has a length and width that is dimensioned to be at least the sameas or larger than a corresponding length and width of the solar cellsubstrate.
 17. The cover system of claim 12, wherein the seal member isfoam rubber having a cross-sectional shape selected from the groupconsisting of an o-ring and a d-ring, and wherein the seal member isconfigured to engage the peripheral angled edges of the solar cellsubstrate about mid-way between lateral sides of the seal member.
 18. Amethod for fabricating solar cells, the method comprising: depositing aconductive bottom electrode layer on a top surface of a substrate;depositing an absorber layer on the bottom electrode layer; performingselenization on the absorber layer; protecting the absorber layer byplacing a protective cover on the top surface of the substrate, whereina resiliently deformable seal member on the cover engages peripheralangled edges of the substrate to effectuate a leak-resistant seal; andwet etching a bottom surface of the substrate with the protective coverpositioned on the top surface of the substrate to remove selenizationcompound deposits.
 19. The method of claim 18, further comprisingrinsing the substrate with deionized water after wet etching and airdrying the substrate after rinsing.
 20. The method of claim 19, furthercomprising removing the cover from the substrate after rinsing and airdrying.